Roller bearings have a greater loading capability of a radial load than ball bearings, and tapered roller bearings in which truncated conical rollers (tapered rollers) as rolling elements are incorporated can support a combined load of a radial load and an axial (thrust) load. For this reason, the tapered roller bearings are widely used for rotary supports of various mechanical apparatuses (e.g., see Patent Document 1).
As cages used for the tapered roller bearings, metal cages formed by press-molding a steel sheet or resin cages formed by injection-molding a thermoplastic resin filled with a reinforcement such as glass fiber or carbon fiber are used. Especially, the resin cages have an advantage of having lightness and mass-productivity, an advantage of not generating worn metal powder or the like, and so on, and thus are widely used. The resin cages are often injection-molded using a metal mold structure in which a pair of metal molds are separated in an axial direction, that is, an axial draw type mold in order to cut down manufacturing costs (e.g., see Paragraph [0011] and FIG. 11 of Patent Document 1).
In the cages injection-molded by this axial draw type mold, since the cage generally has a shape in which, on the basis of each mold parting line inside each pocket which is made to be a boundary, one side is generally in contact with a tapered roller and the other is not in contact with the tapered roller, the tapered roller can be inserted from an inner diameter side, and does not fall off from an outer diameter side but falls off from the inner diameter side.
Therefore, since the tapered roller falls off with the cage and the tapered roller alone, productivity of the tapered roller bearing is lowered depending on a configuration of an assembly line.
As illustrated in FIG. 16, in a resin cage 110 for a tapered roller bearing set forth in Patent Document 2, a mold parting plane A extending in an axial direction is formed at a pillar part 113 of the cage 110. Inner diameter-side conical surfaces 115A are formed closer to inner diameter-side portions than a virtual conical plane C connecting rotation axes of a plurality of rollers 104 on an outer diameter side from the mold parting plane A on facing surfaces of neighboring pillar parts 113, and radial planes 116A are formed closer to outer diameter-side portions than the virtual conical plane C. In addition, outer diameter-side conical surfaces 115B are formed closer to the outer diameter-side portions than the virtual conical plane C on an inner diameter side from the mold parting plane A, and radial planes 116B are formed closer to the inner diameter-side portions than the virtual conical plane C. Thereby, a tapered roller 104 is retained on both the outer diameter side and the inner diameter side of the mold parting plane A while performing injection molding by an axial draw type mold, and falling of the tapered roller 104 is prevented.